Method of concentrating and removing harmful substance using double-stranded dna and adsorbent and apparatus therefor

ABSTRACT

There is provided a method of removing harmful substance characterized by comprising contacting a harmful substance-containing liquid to be treated with a double-stranded DNA, adsorbing the harmful substance onto the double-stranded DNA through intercalation, and separating it. The method is particularly useful for removing dioxins, and can be carried out by contacting a liquid to be treated with an adsorbent comprising a double-stranded DNA or a solution containing a double-stranded DNA enclosed in a container or a bag made of a membrane that is permeable for the harmful substance but is not permeable for the double-stranded DNA.

TECHNICAL FIELD

The present invention relates to a method and an apparatus in which aharmful substance, particularly dioxins are concentrated and/or removedfrom a liquid such as water, milk or breast milk, etc. by using of adouble-stranded DNA.

BACKGROUND ART

Dioxins including polychlorinated dibenzo-p-dioxin (PCDD),polychlorinated dibenzofuran (PCDF) and coplanar polychlorinatedbiphenyl (PCB) are harmful substances that are taken in through foodchain and accumulated in a number of organisms. As these dioxins areliable to have an adverse effect on human body even in an extremelyslight amount, it is an important subject to inhibit generation ofdioxins and remove dioxins from a polluted environment. In particular,dioxins in water such as rivers or lakes, etc. are present in a statewhich dioxins are adhered on the surface of insoluble fine particles orin a state which dioxins are dissolved in water. The former could beremoved by aggregating with the fine particles, but the latter was verydifficult to be removed.

Means for removing dioxins dissolved in water includes a removal ofdioxins by charging a liquid to be treated into a membrane separationapparatus in which active carbon is fluidized, adsorbing dioxinsdissolved in water on the active carbon, and removing solid contentssuch as the active carbon or suspended substance, etc. by membraneseparation and thereby removing dioxins (for example, see JP A2002-239347). In this means, dioxins can be removed by adsorbingdissoluble dioxins on active carbon, and filtering dioxins adsorbed onthe active carbon and solid contents through a membrane.

An object of the present invention is to provide a method in which aharmful substance such as dioxins dissolved in water, milk or breastmilk, etc. can be removed in an efficient manner and at a low cost; aharmful substance adsorbent used therefor, and an apparatus usedtherefor.

DISCLOSURE OF INVENTION

The present inventors, as a result of eager research, found that harmfulsubstance dissolved in liquid such as water, milk or breast milk, etc.can be efficiently concentrated and/or removed by taking advantage ofso-called intercalation that an aromatic compound having a planarstructure is inserted between base pairs of double-stranded DNA havingdouble helix structure, and completed the present invention.

Therefore, the present invention relates to a method of removing harmfulsubstance characterized by comprising contacting a harmfulsubstance-containing liquid to be treated with a double-stranded DNA,adsorbing the harmful substance onto the double-stranded DNA throughintercalation, and separating it.

In addition, the present invention relates to an adsorbent used for themethod of removing harmful substance, comprising a double-stranded DNAor a solution containing a double-stranded DNA enclosed in a containeror a bag made of a membrane that is permeable for the harmful substancebut is not permeable for the double-stranded DNA.

Further, the present invention relates to an apparatus for removingharmful substance, which is used for the method of removing harmfulsubstance and which comprises a contact bath having at least two spacesthat is divided by a membrane that is permeable for a harmful substancebut is not permeable for a double-stranded DNA; a double-stranded DNAsolution circulating means for circulating a double-stranded DNAcontaining solution and flowing the double-stranded DNA containingsolution in one space through the membrane; and a means for circulatinga liquid to be treated, for circulating a harmful substance-containingliquid to be treated, and flowing the liquid to be treated in the otherspace through the membrane, and wherein the harmful substance istransmitted through the membrane from the liquid to be treated to thedouble-stranded DNA containing solution, and separated; and also relatesto an apparatus for removing harmful substance characterized bycomprising a contact bath having an adsorbent containing adouble-stranded DNA in non-free state; and a means for circulating aliquid to be treated, for circulating a harmful substance-containingliquid to be treated, in such a manner that the liquid is flown in thecontact bath, and wherein the adsorbent comprises a double-stranded DNAor a solution containing a double-stranded DNA enclosed in a containeror a bag made of a membrane that is permeable for the harmful substancebut is not permeable for the double-stranded DNA, and wherein theharmful substance is transmitted from the liquid to be treated to theadsorbent, and separated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of an apparatus forremoving harmful substance according to the present invention;

FIG. 2 is a schematic view showing an embodiment of the contact bath inFIG. 1;

FIG. 3 is a schematic view showing another embodiment of an apparatusfor removing harmful substance according to the present invention; and

FIG. 4 is a perspective view showing an embodiment of an adsorbentaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The double-stranded DNA used in the present invention is composed of twopolynucleotide chains having right-handed helix. Planar bases havingstructural complementarity each other project from the sugar-phosphatebackbones of the two polynucleotide chains perpendicularly to thehelical axis toward the center of the helix, and are attached byhydrogen bonds. There are gaps of a width of ca. 1.1 nm and a height ofca. 0.34 nm between base pairs of the double-stranded DNA in case of Btype structure, small molecules having planar structure can be insertedin the gaps, and this is called intercalation. This phenomenon isoccasionally accelerated by the electric charge or hydrophobicity of thesmall molecules. As dioxins have a planar structure consisting of pluralbenzene rings and show hydrophobicity, it is anticipated to removedioxins from water by use of double-stranded DNA.

As the above-mentioned double-stranded DNA, for example ones in whichmilt of fish is used as raw material can be used. It is known that themilt of fish contains double-stranded DNA and proteins in quantity, andis very nutritious food material. However, a very small part of the miltof fish is only utilized as food eaten in the fresh, and the area inwhich it is used is limited due to difficulty of processing, storagestability or the like, and the majority thereof has been discarded. Inparticular, the milt of salmon landed in quantity at Hokkaido in Japanhas been used as animal feeding stuff or plant food or discarded in anamount of 10,000 tons or more per year. Therefore, the milt of fishcontaining a large amount of double-stranded DNA is particularlysuitable as raw material for a large-scale production of double-strandedDNA in a low cost. The fish includes for example salmon, herring, trout,cod and the like. Double-stranded DNA can be obtained by removing skin,muscle, vein and the like from these milt, then purifying it to deleteoil contents.

Although the harmful substance that can be treated according to thepresent invention includes ones over a wide range, organic compoundshaving flat steric structure, such as compounds having aromatic ring canbe preferably treated due to the use of intercalation intodouble-stranded DNA. Particularly, the present invention is preferablyapplied in the treatment of dioxins such as dibenzo-p-dioxin (DD),dibenzofuran (DF), biphenyl (BP), polychlorinated dibenzo-p-dioxin(PCDD), polychlorinated dibenzofuran (PCDF), coplanar polychlorinatedbiphenyl (PCB) or the like.

In the method of removing harmful substance according to the presentinvention, the manner of contacting a liquid to be treated withdouble-stranded DNA is not specifically limited, and includes forexample a process in which a liquid to be treated and double-strandedDNA are contacted through a membrane that is permeable for harmfulsubstance but is not permeable for the double-stranded DNA so that thedouble-stranded DNA may not pass into the liquid to be treated. In thisprocess, contact area between a double-stranded DNA containing solutionand the liquid to be treated can be increased by using the membrane in aform of hollow thread, and thus treatment efficiency of liquid to betreated can be improved.

The manner of contacting a liquid to be treated with double-stranded DNAalso includes a process in which an adsorbent containing adouble-stranded DNA in non-free state is contacted with the liquid to betreated. In this process, the liquid to be treated is charged in areceiving bath, and the adsorbent is introduced in the receiving bath.Optionally, it is preferable to circulate or stir the liquid to betreated in the receiving bath to increase in the contact efficiencybetween the adsorbent and the liquid to be treated.

The adsorbent includes for example a gel formed by immobilizingdouble-stranded DNA in an acrylamide gel. The gel can be formed in acylindrical shape, disk shape or the like. In addition, a bead-shapedgel having generally uniform particle diameter can be formed dependingon the process of producing the gel. Further, other embodiments of theadsorbent include one formed by immobilizing double-stranded DNA inpolysulfone. Polysulfone can be easily formed in bead shape, laminateshape or the like. Particularly, the adsorbent formed by immobilizingdouble-stranded DNA in polysulfone formed in a shape of hollow threadhas a large contact area with the harmful substance-containing liquid tobe treated and is improved in treatment efficiency.

The specific embodiment of the adsorbent is one comprising adouble-stranded DNA or a solution containing a double-stranded DNAenclosed in a container made of a membrane that is permeable for theharmful substance but is not permeable for the double-stranded DNA. Inthe adsorbent, the harmful substance in the liquid to be treatedpenetrates the membrane and is adsorbed on double-stranded DNA, on theother hand, as the double-stranded DNA does not penetrate the membrane,the harmful substance can be transmitted to the double-stranded DNAcontaining solution and efficiently removed.

Further, in the present invention, the harmful substance intercalatedinto double-stranded DNA can be desorbed from the double-stranded DNA byextraction with an organic solvent. The double-stranded DNA containingsolution or the double-stranded DNA containing adsorbent can be re-usedby regeneration.

Hereinafter, the present invention is described in more detail byreference to drawings. FIG. 1 is a schematic view showing an embodimentof an apparatus for removing harmful substance according to the presentinvention, FIG. 2 is a schematic view showing an embodiment of thecontact bath in FIG. 1, FIG. 3 is a schematic view showing anotherembodiment of an apparatus for removing harmful substance according tothe present invention, and FIG. 4 is a perspective view showing anembodiment of an adsorbent according to the present invention.

The apparatus for removing harmful substance according to the embodimentshown in FIG. 1 is composed of a circulating means of double-strandedDNA containing solution 2, a circulating means of liquid to be treated3, and a contact bath 1 connected to the circulating means ofdouble-stranded DNA containing solution 2 and the circulating means ofliquid to be treated 3.

The circulating means of double-stranded DNA containing solution 2 isfor example a pump for circulating a double-stranded DNA containingsolution, and the double-stranded DNA in the solution functions assubstance for adsorbing harmful substance in the apparatus for removingharmful substance according to the present invention. The concentrationof the double-stranded DNA containing solution is about 0.1 to 10 μM(bp), for example, depending on the amount of harmful substance to betreated, time in which treatment should be completed, or the like.

The circulating means of liquid to be treated 3 is for example a pumpfor circulating the liquid to be treated containing harmful substance tobe concentrated and/or removed from water. The concentration of harmfulsubstance in the liquid to be treated is not specifically limited, andfor example even when the harmful substance is present in an extremelylaw concentration of ppb level, the apparatus for removing harmfulsubstance according to the present invention permit an efficienttreatment.

The contact bath 1 has a membrane that is permeable for harmfulsubstance but is not permeable for double-stranded DNA, and the interiorof the contact bath 1 is divided into at least two spaces with themembrane. And, a double-stranded DNA containing solution is circulatedin the one space, while a liquid to be treated is circulated in theother space. For the membrane, can be used for example a semipermeablemembrane having a pore size through which small molecules having amolecular weight of some hundreds, like dioxins penetrate but macromolecules having a molecular weight of 5 million or more do notpenetrate, and such a semipermeable membrane can be commerciallyavailable.

The mode for dividing the space in the contact bath 1 by providing themembrane is not specifically limited so long as both the double-strandedDNA containing solution and the liquid to be treated can be circulatedand both of them can be contacted. For example, the following structurescan be applied: a simple structure in which the contact bath 1 isdivided into two spaced by one membrane, a structure in which thecontact bath 1 is divided into upper and lower parts, or a structure inwhich the contact bath 1 is divided in a form of doughnut so as tobecome a cylindrical double bath. However, from viewpoint of thetreatment principal of the apparatus for removing harmful substanceaccording to the present invention, the larger the contact area betweenthe double-stranded DNA containing solution and the liquid to be treatedbecomes, the higher the treatment efficiency becomes. Therefore, forexample, as shown in FIG. 2, the contact bath 1 in which either thedouble-stranded DNA containing solution or the liquid to be treated ispassed inside a number of hollow threads 5 made of semipermeablemembrane and the other is passed outside the hollow threads 5, isimproved in the contact area between the double-stranded DNA containingsolution and the liquid to be treated, and thereby showing a hightreatment efficiency.

The removal of harmful substance by use of the apparatus for removingharmful substance having the above-mentioned constitution is carried outby circulating a double-stranded DNA containing solution in one space ofthe contact bath 1 by the circulating means of double-stranded DNAcontaining solution 2, and on the other hand by circulating a liquid tobe treated in the other space of the contact bath 1 by the circulatingmeans of liquid to be treated 3. In this process, the liquid to betreated may be circulated directly from lakes, water tanks or the likestoring liquid to be treated, or may be circulated after it wastransferred to a water tank. In addition, each liquid may be circulatedto arbitrary directions. Consequently, a double-stranded DNA containingsolution and a liquid to be treated are contacted in the contact tank 1through the membrane, harmful substances such as dioxins contained inthe liquid to be treated penetrate the membrane in the contact bath 1and are intercalated into the double-stranded DNA contained in thedouble-stranded DNA containing solution. The double-stranded DNA intowhich harmful substances are intercalated does not penetrate themembrane, and therefore harmful substances are removed from the liquidto be treated, and concentrated in the double-stranded DNA containingsolution.

The harmful substances concentrated in the double-stranded DNAcontaining solution are finally treated by any known methods such asincineration. In addition, when the double-stranded DNA containingsolution that contains the double-stranded DNA into which harmfulsubstances are intercalated is mixed with an organic solvent such ashexane, the harmful substances intercalated into the double-stranded DNAare desorbed from the double-stranded DNA, and transferred to theorganic solvent. According to the above-mentioned process, thedouble-stranded DNA into which harmful substances are intercalated tosaturation can be also regenerated.

The apparatus for removing harmful substance having the embodiment shownin FIG. 3 is composed of a circulating means of liquid to be treated 3,and a contact bath 1 connected to the circulating means of liquid to betreated 3 and containing an adsorbent 4.

The adsorbent 4 contains double-stranded DNA without liberation thereof,and is obtained by chemically linking the double-stranded DNA on acarrier such as a high-molecular weight compound. The shape thereof isnot specifically limited, and may be spherical, fiber-like, sheet-likeor the like. For improving contact efficiency between double-strandedDNA and liquid to be treated, is preferable the adsorbent obtained bylinking a double-stranded DNA on the surface of a porous carrier. Inaddition, can be also used the adsorbent 4 obtained by filling adouble-stranded DNA containing solution containing a double-stranded DNAin bag made of semipermeable membrane that is permeable for harmfulsubstance but is not permeable for the double-stranded DNA.

The removal of harmful substance by use of the apparatus for removingharmful substance having the above-mentioned constitution is carried outby placing the adsorbent 4 in the contact bath 1, and circulating aliquid to be treated in the contact bath 1 by the circulating means ofliquid to be treated 3. Consequently, harmful substances such as dioxinscontained in the liquid to be treated are intercalated into thedouble-stranded DNA contained in the adsorbent 4, and thus harmfulsubstances are removed from the liquid to be treated. Next, theadsorbent 4 in which harmful substances are adsorbed is taken out of thecontact bath 1, and treated by any known processes.

Further, in case where the activity for adsorbing harmful substance ofthe adsorbent 4 is lowered, the circulation of the liquid to be treatedis stopped, and an organic solvent is circulated in the contact bath 1,thereby desorbing and transferring the harmful substances from theadsorbent 4 containing double-stranded DNA into which harmful substancesare intercalated to the organic solvent. Consequently, the adsorbent 4is regenerated, and the harmful substances are extracted in the organicsolvent.

The adsorbent 4 shown in FIG. 4 is obtained by enclosing adouble-stranded DNA or a double-stranded DNA containing solution in acontainer or a bag made of a membrane that is permeable for the harmfulsubstance but is not permeable for the double-stranded DNA. As themembrane, any semipermeable membrane that is permeable for a harmfulsubstance but is not permeable for a double-stranded DNA can be used. Anadsorbent can be produced by preparing for example a bag made of thesemipermeable membrane, and enclosing a double-stranded DNA or asolution containing a double-stranded DNA in a desired concentration soas not to leak. The bag can be formed for example by pasting membranestogether to produce a tubular body and sealing the top and bottomthereof.

EXAMPLE 1 Removal of Dioxins by Use of Double-Stranded DNA ContainingSolution

A solution containing dioxins of dibenzo-p-dioxin (DD), dibenzofuran(DF) and biphenyl (BP) in a concentration of 1 mg/ml respectively wasprepared as a model liquid to be treated. The model liquid to be treatedwas contacted with a double-stranded DNA containing solution containingdouble-stranded DNA originating from salmon milt in a concentration of6.8 μM (bp) through a semipermeable membrane for 96 hours at a flow rateof 100 ml/minute.

Upon completion of the contact, the concentrations of dioxins in themodel liquid to be treated and the double-stranded DNA containingsolution were compared, and it was found that the dioxin concentrationof the double-stranded DNA containing solution was some hundreds timesthat of the model liquid to be treated and that dioxins wereconcentrated in the double-stranded DNA containing dioxins.

Next, hexane was added into a double-stranded DNA containing solutioncontaining dioxins in a high concentration and penetrated at roomtemperature for 6 hours. This enabled extraction of dioxins into hexane.The harmful substance removing activity of the double-stranded DNAcontaining solution regenerated as above was nearly equal to that of thedouble-stranded DNA containing solution that had not been contacted withthe liquid to be treated.

EXAMPLE 2 Production of Adsorbent

A solution of a double-stranded DNA containing solution containingdouble-stranded DNA originating from salmon milt in 6.8 mM (bp) wasprepared. A bag having a size: length of 10 cm, width of 5 cm andthickness of 2 cm was also formed from dialysis membrane of 1 kDcut-off. Each of the bags was filled with 50 ml of the solution andsealed to produce adsorbents.

INDUSTRIAL APPLICABILITY

According to the present invention, harmful substances such as dioxinsdissolved in water, milk or breast milk, etc. can be efficientlyconcentrated and/or removed by intercalating the harmful substancesbetween base pairs of a double-stranded DNA. Further, as thedouble-stranded DNA, can be used those originating from the milts offishes the most part of which had been discarded conventionally.Therefore, treatment cost can be lowered.

1. A method of removing harmful substance characterized by comprisingcontacting a harmful substance-containing liquid to be treated with adouble-stranded DNA, adsorbing the harmful substance onto thedouble-stranded DNA through intercalation, and separating it.
 2. Themethod of removing harmful substance according to claim 1, wherein theharmful substance is dioxins.
 3. An adsorbent used for the method ofremoving harmful substance according to claim 1, characterized bycomprising a double-stranded DNA or a solution containing adouble-stranded DNA enclosed in a container or a bag made of a membranethat is permeable for the harmful substance but is not permeable for thedouble-stranded DNA.
 4. An apparatus for removing harmful substance,which is used for the method of removing harmful substance according toclaim 1, characterized in that comprises a contact bath having at leasttwo spaces that is divided by a membrane that is permeable for a harmfulsubstance but is not permeable for a double-stranded DNA; adouble-stranded DNA solution circulating means for circulating adouble-stranded DNA containing solution and flowing the double-strandedDNA containing solution in one space through the membrane; and a meansfor circulating a liquid to be treated, for circulating a harmfulsubstance-containing liquid to be treated, and flowing the liquid to betreated in the other space through the membrane, and wherein the harmfulsubstance is transmitted through the membrane from the liquid to betreated to the double-stranded DNA containing solution, and separated.5. The apparatus for removing harmful substance according to claim 4,wherein the membrane is formed of hollow threads, and the contact bathis divided into a space outside the hollow threads and a space insidethe hollow threads.
 6. An apparatus for removing harmful substance,which is used for the method of removing harmful substance according toclaim 1, characterized in that comprises a contact bath having anadsorbent containing a double-stranded DNA in non-free state; and ameans for circulating a liquid to be treated, for circulating a harmfulsubstance-containing liquid to be treated, in such a manner that theliquid is flown in the contact bath, and wherein the adsorbent comprisesa double-stranded DNA or a solution containing a double-stranded DNAenclosed in a container or a bag made of a membrane that is permeablefor the harmful substance but is not permeable for the double-strandedDNA, and wherein the harmful substance is transmitted from the liquid tobe treated to the adsorbent, and separated.